Question

Choose the incorrect statement from the following.

• A. In birds and mammals, internal fertilisation takes place
• B. Colostrum contains antibodies
• C. Polyspermy in mammals is prevented by the chemical changes on the egg surface
• D. In the human female, implantation occurs almost seven days after fertilisation

Hint:

In mammals, polyspermy is prevented mainly by changes in the zona pellucida after fertilisation.

Answer 1

The Correct Option is C

Concept:
Fertilisation in mammals includes the fusion of sperm and ovum. After one sperm enters the ovum, mechanisms are activated to prevent entry of more sperms. This prevention of entry of multiple sperms is called prevention of polyspermy.

Step 1: Check statement (A).
Birds and mammals show internal fertilisation. So, statement (A) is correct.

Step 2: Check statement (B).
Colostrum is the first milk produced after childbirth. It contains antibodies and provides immunity to the newborn. So, statement (B) is correct.

Step 3: Check statement (D).
In humans, implantation begins about 6 to 7 days after fertilisation. So, statement (D) is correct.

Step 4: Check statement (C).
In mammals, prevention of polyspermy mainly occurs due to changes in the zona pellucida after sperm entry. The statement says chemical changes on the egg surface, which is not the most accurate description in standard NCERT terminology. Therefore, statement (C) is taken as the incorrect statement.

Step 5: Final conclusion.
The incorrect statement is: \[ \boxed{\text{(C)}} \]